Method of drawing stainless steel wire



patented Aug. 15,1950 7 METHOD or DRAW can is. Fessler, Cleveland, ()hib, sssig'nor w The American Steel and Wire company of New Jersey, a corporation of New Jersey Ne Drawing. iiiipiicati' jn stir-i123, 1945, Serial No. 589,934

drawing wire from stainless steel rod and wire stock having scale on its surface of the type-pro duced by hot working and annealing under oxidizing conditions. This type of scale is formed on stainless steel rod hot rolled from a billet in air in the currently conventional manner, and also by annealing stainless steel rod and wire when no effective protection is provided against air while it is at annealing temperatures. It is the type of scale" whichprior to this invention: had to be removed by pickling before-the steel could be cold drawn into wire through a, wire drawing die, because its brittle and abrasive naturemade drawing through dies commercially impracticable; The stainless steel with which the invention is concerned is any of the ferritic grades containing at least 12% chromium and any of the austenitic grades; allcf: these grades producing the described scale type in forms that make it harder tore'move than do the forms pro ducedon plain carbon. and: low alloy steels, and which make itmore destructive to wire drawing dies. Also, these stainless grades are inherently harder to' draw than the other steels named, and prior to this invention they not only required more expensive pickling toiremove the scale, but also required the extra steps of lead coating to permit their drawing; andthe subsequent removal of the lead My invention provides a process for treating this type of scale so that it may not only be left :on stainless? steel ro'd and wire during cold drawing through awire'drawing die, but also that it will beconditioned tov permit drawing of such rodand wire without lead coating the latter.

The principles of the invention may be understood from.- the following description of specific examples;

To cite one example, ie'rr-itic stainless'steel of the straight 12% chromium grade is hot rolled" in air from a billet into a inch diameter rod in the currently conventional fashion" so its surface has the'describ e'dtype of scale. Then the cold rod bundle is immersed in a: strongly alkaline-water solution heated to from 180 F. to boil ing temperature, thebundle being left in this solution for from 20 to 30 minutes. Next, while still wet with such a solution, the bundle isliined in the usual manner excepting that baki'ng is necessary only to dry the lime solution. Finally, the rod fromthe bundle 'is dry drawn through tungsten carbide wire drawing dies using a lubri'cant consisting by weight of 80%" calciumstearate, 15% graphite and 5% dry lime intimately.

volving heavier reductions in the first draft and with the succeeding draft-reductions becoming lighter by comparison, with the first; as the draw 9 Claims. (01. res-s35) ing" progresses and the stock work hardens. The redis 9%; inch diameter and it is drawn in three drafts down to .192 inch diameter before anneal-- ing is required by the work hardening effect. lrnnealmg is then carried out without cleaning thest'o'ck and with air contacting the stock at annealing temperatures to develop more of the described type or scale, and the stock is then again treated, limed and lubricated as described and: drawn down in one draft to' .1875 diameter which is the finished slze. At this time simple acid cleaning with a water solution of either hy drofiuori'c; hydrochloric, sulphuric acids, etc., suffic'es to" remove the scale} lime and lubricant left on thefinishedzwire.

As a second example, austenitic stainless steel of the 18-8 grade is similarly hot rolled into rods having a" diameter of of an inch, but since this grade must be stabilized against carbide pre cip'itation by, quenching from temperatures around 2100" F., the rod is heated to these temperatures and then quenched by passing it continuously through a strongly alkaline water solution to both stabilize it and condition its scale for drawing, as was done in the first example by the more prolonged immersion. That is to say, ferritic steels cannot be quenched because they wouldharden, so the bundle is immersed cold into the heated solution and so requires time to heat'to'th'e solution temperature, while austenitic'steels'often must and always can be quenched from very hightemperatures. In the case of austeni-tic steel. therefore, it is enough to let the solution-contact the rod for 5' seconds, remembering the continuous nature of the immersion, and when removedthe heat left in the rod dries it; Therefore, the rod is again wet withthe solutionbeiore the liming, or is treated ,with some other agent promoting wetting of the rod with the lime solution during liming.- It has been iound preferable inall instances to have the rod; wet with some good wetting agent prior to liming. Otherwise than noted, the 18-8 rodmay bedrawn and cleaned as was the straight 12%chromium grade.

Now it will be noted that these examples show that one characterizing feature of the inventionis the discovery that the scale which in commercial practices is always forrned as the result of processing the" steel into rod or by its heat treatment and which has caused so much trouble in thepast is conditioned sothat it notonly ceases to cause trouble, so it need not be removed, but also actuallysubstitutes for the lead coatingformerly necessary when the higher alloy stainless steel grades were die worked. I It is thus' pertinent to more fully discuss the strongly alkaline water solution used for this conditioning.

,Thi solutionmay be made of any alkaline substance providing the'sol ltiorr with suificient al asiaiaf kalinity, and the degree of alkalinity may be detern-lined simply by following the procedure described and adjusting the alkalinity until a value is found which makes possible successful drawing of the scaled rod. The requireddegree of alkalinity varies with the immersion time of the scaled rod in the solution and with the solution temperature, a lower degree being required with longer immersion time and higher temperatures and vice versa. However, the time in both batch handling and continuous immersion is limited in commercial work, and the solution temperature cannot exceed its boiling point, so the solution should be strongly alkaline. To examplify, by using a commercially availabl alkaline detergent consisting by weight of 42.86% Na2CO3, 7.41% NaOH, 2.85% Na2Si409, 14.22% Na3Po4.2I-I2O and 32.66% rosin soap; from 5 to 8 ounces of this detergent to a gallon of water provides a degree of alkalinity making effective the time values given in the two specific examples. A water solution of sodium hydroxide or sodium carbonate providing a similar degree of alkalinity may be substituted. Another commercial available alkaline detergent consists by weight of 41.40% NazCOc, 29.60% Na3PO42I-IZO and 29% rosin soap; and about 5 to 8 ounces per gallon of water provides a solution that is also effective. In no event should the immersion time be so long as to remove substantial amounts of the scale being treated to make it substitute .for lead coating during the drawing.

As indicated, it .is important that such a solution also be .used to wet the rod and wire stock prior to liming, but this solution may be applied to the scaled stock cold when considered only for use as a wetting agent during the liming. If possible the stock is preferably limed while still wet from its treatment with the solution at elevated temperature to condition its scale for drawing, but if it dries it should be rewet with the solution or its equivalent prior to the liming.

The lubricant used must be of such a nature as to function as a wire drawing lubricant under the heavy pressures and consequently high temperatures encountered in drawing the high alloy stainless steel-grades here involved, and the one specifically described does this. 7 Others maybe substituted providing they do not fail to function as a wire drawing lubricant during the cold drawing through the Wire'drawing die. For instance, any metallic stearate and graphite may be used, if the graphite is covered with the stearate. a

' In the foregoing it-is to be noted that certain annealings under oxidizing conditions are mentioned, and these may be for the usual purposes common to the'prior art. Thus, in the caseof the straight chromium stainless ferritic steel type, although not mentioned before, it is common to batch anneal the hot-rolled rod bundles by passing them through a continuous furnace directly heated by flames from burners supplied with natural gas to normalize the steel by heating it to from about l500 to 1700 F., and slowly cooling it, prior to any drawing, and, as specifically mentioned, to anneal the wire in process when it work hardens to a degree requiring this, and here again the process wire in coils is batch annealed continuously as described. As to the austenitic type, the practice is to anneal the hotrolled ro'd or process wire bundles by causing the rod or process wire to continuously uncoil and pass through a similar continuous furnace as a single strand, so it is heated to around 2100 F 4 whereupon it is quenched continuously upon leaving the furnace, this being for the reason described and also because this is the way the austenitic stainless steel types must be annealed even when chemically stabilized against carbide precipitation.

Both types of furnaces are provided with air and gas valves for controlling the gas-to-air ratio of the gas and air mixture fired by the open flame burners inside the furnace, and it is common in the art to say that the furnace atmosphere, provided by the air leaking into the furnace and the products of combustion, is oxidizing, neutral or reducing, depending on whether the air is excessive, just suficient, or insufficient, for

always oxidizing to varying degrees respecting all stainless steels.

Using the above terminology, the usual method of operating such furnaces, in heating stainless steel for annealing, has been to use an oxidizing atmosphere, this meaning too much air for comhot-rolled stainless steel rod of either the feri to the furnace operators.

ritic or austenitic types is annealed prior to the described conditioning of its scale, in one or the other of the described types of furnaces with the furnace air and gas valves adjusted to provide a furnace atmosphere that is at least slightly reducing respecting iron or, more specifically, so it contains from a fraction of one per cent up to about six or seven per cent of carbon monoxide in excess of that which can be burned with the as a standard. It will put the described type of scale on stainless steel if it is not already present.

With the present invention, the furnace air and gas valves are also adjusted to give such a reducing atmosphere during the annealing of the process wire or of cleaned wire to be further drawn, and this practice is followed in the case of both the ferritic and austenitic types of stainless steel.

Except for the foregoing difference, the recently developed method of cold die working scaled stainless steel is practiced as described, but in the case'of the present invention it will be found that because of this difference the treatment in the alkaline water solution unexpectedly results in a critically improved scale of markedly better cold die drawing characteristics It has better adherence to the rod or wire and is less abrasive to the dies, This is so even when normally scaled hot-rolled rod is annealed as described the annealing in an atmosphere having 7 excess carbon monoxide, or which is reducing in the terminology of the art, cooperating with the described conditioning to attain this new and unexpected result in all instances.

As used in the Specification and claims, the term scaled is intended to mean that the stock carries a substantial surface coating of oxide.

I claim:

1. In the art of cold die working stainless steel stock having scale on its surface of the type produced by its hot working and annealing under oxidizing conditions, the improvement comprising annealing said scaled stock in a slightly reducing atmosphere respecting iron, thereby changing the character of the scale, contacting said scale on said annealed stock with a strongly alkaline water solution at elevated temperature for a time less than that required to remove substantial amounts of said scale from said stock, lubricating the scaled stock and cold die work ing thescaled and lubricated stock.

2. In the art of drawing wire from austenitic stainless steel rod and. wire stock having the scale on its surface of the type produced by its hot Working and annealing under oxidizing conditions, the improvement comprising heating said scaled stock to a temperature where its carbides are in solution in a slightly reducing atmosphere respecting iron to change the character of the scale and then quenching it by continuously passing it through a strongly alkaline water solution, liming the scaled stock, lubricating the scaled and limed stock, and cold drawing the scaled, limed and lubricated stock through a wire drawing die.

3. In the art of drawing wire from ierritic stainless steel rod and wire stock havin scale on its surface of the type produced by its hot working and annealing under oxidizing conditions, the improvement comprising annealing said scaled stock in a slightly reducing atmosphere respecting iron, thereby changing the character of the scale, immersing the scaled stock in a strongly alkaline Water solution at temperatures between 180 F. and its boiling point for from to 39 minutes, liming the scaled stock, lubricating the scaled and limed stock, and cold drawing the scaled, limed and lubricated stock through a wire drawing die.

4. In the art of drawing wire from stainless steel rod and wire stock having scale on its surface of the type produced by its hot working and annealing under oxidizing conditions, the improvement comprising annealing said scaled stock in a slightly reducing atmosphere respecting iron, thereby changing the character or the scale, contacting the scale with a strongly alkaline water solution at elevated temperature, liming the stock while wet with this solution, lubricating the scaled and limed stock witha mixture of metallic sterate and graphite with the metallic stearate coating all the graphite particles,

and cold drawing the scaled, limed and lubricated stock through a wire drawing die, the alkalinity, temperature and time of said contactin being adjusted so the scale draws through said die.

5. In the art of die-working stainless steel stock, the improvement comprising annealing said stock in an atmosphere of combustion gases containing about 2% carbon monoxide so as to form a scale thereon, contacting the scale on said annealed stock with a strongly alkaline water 1 solution at elevated temperature for a time less than that required to remove substantial amounts of said scale from said stock, lubricating the scaled stock and die-working the scaled and lubricated stock while cold.

6. In the art of drawing wire from austenitic stainless steel rod and wire stock, the improvement comprising heating said stock to a temperature at which substantial amounts of its carbides are in solution, in an atmosphere of combustion 1O gases containing from a fraction of 1% to 6% carbon monoxide so as to form a scale on the said stock and then quenching it by continuously passing it through a strongly alkaline water solution, liming the scale stock, lubricating the scaled and and lubricated stock through a Wire-drawing die.

'7. In the art of drawing wire from ferritic stainless steel rod and wire stock, the improvement comprising annealing said stock in an at- 20 mosphere of combustion gases containing from a fraction of 1% to 6% carbon monoxide so as to form a scale thereon, immersing the scaled stock in a strongly alkaline water solution at temperatures of from 186 F. to its boiling te1nperatime for from 20 to minutes, liming the scaled stock, lubricating the scaled limed stock, and cold drawing the scaled, limed and lubricated stock through a wire-drawing die.

8. In the art of drawing wire from stainless 30 steel rod and wire stock, the improvement comprising annealing said scaled stock in an atmosphere of combustion gases containing from a fraction of 1% to 6% carbon monoxide so as to form a scale thereon, contacting the scale with a 5 strongly alkaline water solution at elevated temperature, liming the stock while wet with this solution, lubricating the scaled and limed stock with a mixture of metallic stearate and graphite with the metallic stearate coating all the graphite particles, cold-drawing the scaled, limed and lubricated stock through a wire-drawing die without lead coating the stock, and controlling the alkalinity and temperature of said solution and the time of contact therewith so the scale draws through said die and substitutes for a lead coating.

9. In a method of drawing stainless-steel wire, the steps including annealing stainless-steel wire stock in an atmosphere of combustion gases contalning from a fraction of i% to 6% carbon monoxide, thereby forming on the stock an adherent scale, subjecting the scaled stock to a strongly alkaline water solution for a time less than that required to remove a substantial amount of scale, thereby reducing the abrasiveness of the scale, liming the stock, then lubricating the stock and then cold-drawing it through a reducing die.

CARL H. FESSLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,357,342 Montgomery Sept. 5, 1944 2,363,736 Lynn Nov. 28, 1944 2,369,146 Kingston Feb. 13, 1945 2,369,596 Millen Feb. 13, 1945 2,393,675 Fenner et al Jan. 29, 1946 7 2,400,866 Kronwall May 21, 1946 2,442,223 Uhlig May 25, 1948 

5. IN THE ART OF DIE-WORKING STANLESS STEEL STOCK, THE IMPROVEMENT COMPRISING ANNEALING SAID STOCK IN AN ATMOSPHERE OF COMBUSTION GASES CONTAINING ABOUT 2% CARBON MONOXIDE SO AS TO FORM A SCALE THEREON, CONTACTING THE SCALE ON SAID ANNEALED STOCK WITH A STRONGLY ALKALINE WATER SOLUTION AT ELEVATED TEMPERATURE FOR A TIME LESS THAN THAT REQUIRED TO REMOVE SUBSTANTIAL AMOUNTS OF SAID SCALE FROM SAID STOCK, LUBRICATING THE SCALED STOCK AND DIE-WORKING THE SCALED AND LUBRICATED STOCK WHILE COLD. 